THE STEM 



35 



41. Tendrils of the Pas- 

 sion Flower. 



tendril is known by its position. A tendril from the axis 

 of a leaf, like that of the Passion Flower (Fig. 41), is, of 

 course, a stem, i.e. a 

 branch. 



80. In the young 

 stage, when still ex- 

 tended, tendrils are 

 endowed with motion 

 and with sensitive- 

 ness to contact. 

 Their movements are 

 like those of twining 

 stems, — they de- 

 scribe circles or el- 

 lipses until brought 

 against some object. 



When, by the curving of the tip, a hold has been secured 

 upon this object, the tendril coils in a double spiral. 

 The coil or spiral itself is of importance in all such 

 cases, for its elasticity prevents a sudden stress caused, 

 for example, by a blast of wind, from snapping the 

 tendril off, as might be the result were the tendril 

 straight and already tightly drawn at the moment of 

 onslaught. 



" I have more than once gone on purpose, during a gale, to watch a 

 Bryony growing in an exposed hedge, with its tendrils attached to the 

 surrounding bushes ; and as the thick and thin branches were tossed 

 to and fro by the wind, the tendrils, had they not been excessively 

 elastic, would instantly have been torn off and the plant thrown pros- 

 trate. But as it was, the Bryony safely rode out the gale, like a ship 

 with two anchors down, and with a long range of cable ahead to serve 

 as a spring as she surges to the storm." — Darwin. 



81. The tendrils of the Passion Flower are wonderfully sensitive to 

 slight pressure. In Darwin's experiments, " A bit of platinum wire, J^ 

 of a grain in weight, gently placed on the concave point, caused a 

 tendril to become hooked, as did a loop of soft, thin cotton thread Jj 

 of a grain. The point of a tendril of Passi/lora gracilis began to move 

 distinctly in twenty-five seconds after a touch, and in many cases after 

 thirty seconds." 



